Slope cave leaching of exposed or near-surface mineralized deposits

ABSTRACT

Metal values are extracted by a combination of slope caving and leaching from mineralized deposits at or near the surface of the earth that are uneconomic to work in normal ways either because of excessively low grade or access difficulties, e.g., areas normally encountered at the fringes of open pit mining operations. Undercutting of a slope to induce caving results in effective mass fragmentation of the mineralized material and the formation of a substantially unstratified and highly porous body of fragmented material at the foot of the slope. Application of a leach solution to such body, either as is or leveled and provided with superficial basins for holding a supply of the leach solution, so such solution percolates downwardly through the fragmented and unstratified material, extracts values therefrom which are recovered by collection and processing of the pregnant leach liquor.

[Jite ttes Michaelson et al.

[ SLOPE CAVE LEACHING 0F EXPOSED OR NEAR-SURFACE MINERALIZED DEPOSITS [75] Inventors: Stanley 1). Michaelson; Carl D.

- Broadbent, both of Salt Lake City,

. Utah [73] Assignee: Kennecott Copper Corporation,

I New York, NY.

[22] Filed: May 18, 1972 [21] App]. No.: 254,688

[52] Cl....., 299/5, 75/10] R, 423/27 [51] lint. Cl. E21c 41/14 [58] Field of Search 423/27; 75/101 R 108,

[56] References Cited UNITED STATES PATENTS 3,647,261 3/l972 Stenger et al 75/] 12 3,465,818 9/1969 Dixon 75/l0l R 2,045,092 6/1936 Mitchell 75/111 3,639,003 2/1972 Speddon et al. 299/5 [451 May 7,1974

Primary ExaminerErnest R. Purser Attorney, Agent, or Firm-Philip A. Mallinckrodt [5 7] ABSTRACT Metal values are extracted by a combination of slope caving and leaching from mineralized deposits at or near the surface of the earth that are uneconomic to work in normal ways either because of excessively low grade or access difficulties, e.g., areas normally encountered at the fringes of open pit mining operations. Undercutting of a slope to induce caving results in effective mass fragmentation of the mineralized material and the formation of a substantially unstratified and highly porous body of fragmented material at the foot of the slope. Application of a leach solution to such body, either as is or leveled and provided with superficial basins for holding a supply of the leach solution,

so such solution percolates downwardly through the fragmented and unstratified material, extracts values therefrom which are recovered by collection and processing of the pregnant leach liquor.

4 Claims, 4 Drawing Figures SLOPE CAVE LIEACll-IING OlF EXPOSED OR NEAR-SURFACE MINERALIZED DEPOSITS BACKGROUND OF THE INVENTION 1. Field The invention relates to the recovery of metallic values from mineralized earth materials by leaching.

2. State of the Art The leaching of metallic values from mineralized earth materials, such as ores and the sparsely mineralized materials normally present in mine waste dumps, is not new. Heap leaching of fragmented ore materials has been practiced for many years, as has the leaching of waste dumps normally associated with open pit mining of low grade copper ores. These practices, however, all involve mining and transport of the materials concerned. Fragmentation and leaching of ores in place, as by the implanting of atomic bombs underground and the passing of leach solutions through the fragmented material while still in place, have been proposed but ap pear to have only limited practical application. Slope caving in and of itself is not new.

SUMMARY OF THE INVENTION In accordance with the present invention, exposed slopes of firmly consolidated, mineralized deposits, whether naturally exposed or exposed by open pit mining or quarrying practices, are undercut in such a way as to cave and fragment the mass of consolidated material making up such slopes, thereby forming substantially unstratified and highly pervious bodies of fragmented material at the bottoms of such slopes, which bodies of material are thereupon subjected to leaching. Although in some instances it may be desirable to flatten and cup these bodies of mineralized earth materials by appropriate earth working techniques to provide superficial basins for holding the leach solution, there is no mining or haulage of the mineralized material as ordinarily carried out prior to leaching, nor is there any substantial compaction of the mineralized materials as normally occurs. The pregnant leach liquors flowing from the bases of the bodies of fragmented materials are collected and processed in the usual manner for recovery of the contained metal values.

Long slopes may be caved in successive levels, usually but not necessarily from bottom to top, and the leach solution passed through successive piles.

THE DRAWING Procedures representing the best mode presently contemplated of carrying out the method of the invention are illustrated in the accompanying drawing in which:

FIG. l is a schematic view in vertical section taken perpendicularly through a mineralized slope prepared for caving;

FIG. 2, a similar view following caving;

FIG. 3, another similar view showing one possible approach to leaching of the caved material; and

FIG. d, still another similar view showing an alternative approach to leaching of the caved material.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS In accordance with the invention, we have found that mineralized earth materials occurring in exposed slopes that are caved are effectively broken up and can be subjected to leaching for recovery of metal values with out the usual mining and haulage.

As illustrated in FIG. 1, a triangular wedge 10 of earth material in the protruding toe 11a at the foot of a slope 111 is earmarked for removal on the basis of calculations made from knowledge of applicable stability factors in accordance with techniques known to the art. Bore holes, such as the coyote holes indicated 12, are then driven within such toe 1 1a of the slope and loaded in customary manner with explosive having the necessary force when detonated to displace the wedge 10, so the frontal portion 11b of the slope above the toe 11a will cave of its own weight.

In caving, the consolidated earth material will break up and form a highly pervious, substantially unstratified body 14 of fragmented material through which a leach solution can be run for solubilizing metallic values, see FIG. 2. t

If desired, the body 14 of fragmented material may be cupped by suitable earth-moving equipment, such as a grader, to form superficial basins or ponds, such as 15 and 16, FIG. 3, at its top for the reception of a leach solution 17, which will percolate more or less downwardly through the body of material as is usual in present waste dump leaching practice, or the leach solution may be supplied as a spray 18, FIG. 4', to a substantially undisturbed body from a distributor pipe 19. However applied, the leach solution will be collected at or near the bottom of the body of fragmented material in any suitable manner (not shown) normal to the leaching of mine waste dumps and will be transported, as by pipeline, to a suitable location for the recovery of the metal values picked up in the flow of the leaching solution through such material.

Although specific ways of applying the leach solution to the caved material are illustrated in the drawing by way of example, it should be realized that these are not the only ways. Thus, the solution couldbe injected directly into the pervious body of caved materials by the use of well points or the like.

The slope caving step of the present method, that fragments the material to be leached and enables leaching to be effectively accomplished substantially without further preparation of such material, involves a consideration of slope stability based on the existence of natural or artificial planes of weakness, degree of cohesion, coefiicient of friction, cleft and/or pore water pressures, and existence of stress conditions. Slopes can be caved by altering any one or a combination of these factors, but it is normally only practical to alter stress conditions and cleft and/or pore water.

In carrying out the required slope caving, the procedure will usually include: 1) an engineering determination of the characteristics of planes of weakness, cohesion, and coefficient of friction, using generally accepted field and laboratory procedures; (2) estimation and/or engineering measurement of existing water and stress conditions; (3) calculation of the geometrystability relationships, so as to relate the stability factors of l) and (2) to the estimated stress conditions, as predicted by an elastic mathematical model, such as the two-dimensional finite element model described by Goodman and Taylor at pages 303-320 of Procedures of the 8th Symposium on Rock Mechanics, 1966, and thereby obtain indications of stability or instability of critical zones in the slope; (4) design a caving tech- 3 nique, such as water injection, the driving of coyote holes 12 for blasting, a combination of the two, or some other means for reducing slope stability to the point of caving; and actual implementation of the design.

All of the above procedures will be apparent to those skilled in the art on the basis of known techniques and will result in a mass of unstratified fragmented material, such as 14, FIG. 2, much finer in size than can be obtained by the usual drill hole blasting ordinarily employed in open-cut mining practice, for example. In accordance with this invention, then, leaching is carried out at the location of this highly pervious and relatively finely divided material, and an easily transported leach solution is obtained that is pregnant with the metal values, making it unnecessary to transport the remaining, worthless rock materials from the caved area.

Whereas this invention is here illustrated with respect to preferred specific procedures, it should be understood that various changes may be made without departing from the inventive concepts defined by the claims that here follow.

We claim:

l. A method of recovering, by means of an open cut operation, values of a metal, such as copper, from a leachable mineral containing said values and occurring as a substantially firmly consolidated, surface deposit in sloping terrain, comprising undercutting a portion of said sloping terrain in a manner effective to cause caving of said portion to produce a surface located, substantially unstratified, and highly pervious body of broken earth materials containing said mineral and suitable for immediate leaching; flowing a leach solution for said metal values through the surface-located,

caved earth material while said caved earth material is in substantially undisturbed, unstratified, and highly pervious condition; and recovering the pregnant leach solution that flows from said caved earth material.

2. A method in accordance with claim 1, wherein the leach solution is applied to the body of broken earth materials substantially as caved without disturbance thereof.

3. A method in accordance with claim 2, wherein the leach solution is sprayed substantially uniformly over the superficial surface of the body of broken earth materials.

4. A method in accordance with claim 1, wherein the body of broken earth materials is leveled and cupped to provide basins for holding the applied leach solution. 

1. A method of recovering, by means of an open cut operation, values of a metal, such as copper, from a leachable mineral containing said values and occurring as a substantially firmly consolidated, surface deposit in sloping terrain, comprising undercutting a portion of said sloping terrain in a manner effective to cause caving of said portion to produce a surface located, substantially unstratified, and highly pervious body of broken earth materials containing said mineral and suitable for immediate leaching; flowing a leach solution for said metal values through the surface-located, caved earth material while said caved earth material is in substantially undisturbed, unstratified, and highly pervious condition; and recovering the pregnant leach solution that flows from said caved earth material.
 2. A method in accordance with claim 1, wherein the leach solution is applied to the body of broken earth materials substantially as caved without disturbance thereof.
 3. A method in accordance with claim 2, wherein the leach solution is sprayed substantially uniformly over the superficial surface of the body of broken earth materials.
 4. A method in accordance with claim 1, wherein the body of broken earth materials is leveled and cupped to provide basins for holding the applied leach solution. 